Messages in this thread Patch in this message | | | Date | Wed, 21 May 2014 14:30:23 -0500 | From | John Blackwood <> | Subject | Re: Filesystem lockup with CONFIG_PREEMPT_RT |
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> Date: Wed, 21 May 2014 03:33:49 -0400 > From: Richard Weinberger <richard.weinberger@gmail.com> > To: Austin Schuh <austin@peloton-tech.com> > CC: LKML <linux-kernel@vger.kernel.org>, xfs <xfs@oss.sgi.com>, rt-users > <linux-rt-users@vger.kernel.org> > Subject: Re: Filesystem lockup with CONFIG_PREEMPT_RT > > CC'ing RT folks > > On Wed, May 21, 2014 at 8:23 AM, Austin Schuh <austin@peloton-tech.com> wrote: > > > On Tue, May 13, 2014 at 7:29 PM, Austin Schuh <austin@peloton-tech.com> wrote: > >> >> Hi, > >> >> > >> >> I am observing a filesystem lockup with XFS on a CONFIG_PREEMPT_RT > >> >> patched kernel. I have currently only triggered it using dpkg. Dave > >> >> Chinner on the XFS mailing list suggested that it was a rt-kernel > >> >> workqueue issue as opposed to a XFS problem after looking at the > >> >> kernel messages. > >> >> > >> >> The only modification to the kernel besides the RT patch is that I > >> >> have applied tglx's "genirq: Sanitize spurious interrupt detection of > >> >> threaded irqs" patch. > > > > > > I upgraded to 3.14.3-rt4, and the problem still persists. > > > > > > I turned on event tracing and tracked it down further. I'm able to > > > lock it up by scping a new kernel debian package to /tmp/ on the > > > machine. scp is locking the inode, and then scheduling > > > xfs_bmapi_allocate_worker in the work queue. The work then never gets > > > run. The kworkers then lock up waiting for the inode lock. > > > > > > Here are the relevant events from the trace. ffff8803e9f10288 > > > (blk_delay_work) gets run later on in the trace, but ffff8803b4c158d0 > > > (xfs_bmapi_allocate_worker) never does. The kernel then warns about > > > blocked tasks 120 seconds later.
Austin and Richard,
I'm not 100% sure that the patch below will fix your problem, but we saw something that sounds pretty familiar to your issue involving the nvidia driver and the preempt-rt patch. The nvidia driver uses the completion support to create their own driver's notion of an internally used semaphore.
Some tasks were failing to ever wakeup from wait_for_completion() calls due to a race in the underlying do_wait_for_common() routine.
This is the patch that we used to fix this issue:
------------------- -------------------
Fix a race in the PRT wait for completion simple wait code.
A wait_for_completion() waiter task can be awoken by a task calling complete(), but fail to consume the 'done' completion resource if it looses a race with another task calling wait_for_completion() just as it is waking up.
In this case, the awoken task will call schedule_timeout() again without being in the simple wait queue.
So if the awoken task is unable to claim the 'done' completion resource, check to see if it needs to be re-inserted into the wait list before waiting again in schedule_timeout().
Fix-by: John Blackwood <john.blackwood@ccur.com> Index: b/kernel/sched/core.c =================================================================== --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3529,11 +3529,19 @@ static inline long __sched do_wait_for_common(struct completion *x, long (*action)(long), long timeout, int state) { + int again = 0; + if (!x->done) { DEFINE_SWAITER(wait);
swait_prepare_locked(&x->wait, &wait); do { + /* Check to see if we lost race for 'done' and are + * no longer in the wait list. + */ + if (unlikely(again) && list_empty(&wait.node)) + swait_prepare_locked(&x->wait, &wait); + if (signal_pending_state(state, current)) { timeout = -ERESTARTSYS; break; @@ -3542,6 +3550,7 @@ do_wait_for_common(struct completion *x, raw_spin_unlock_irq(&x->wait.lock); timeout = action(timeout); raw_spin_lock_irq(&x->wait.lock); + again = 1; } while (!x->done && timeout); swait_finish_locked(&x->wait, &wait); if (!x->done)
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